René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"test_threading.test_recursion_limit() does crash (segfault) on Alpine Linux (musl)","articleBody":"Python built with `./configure --with-pydebug --disable-gil` and `gcc -Og` on Alpine Linux (Python built with `musl` C library).\n\nExample of crash on \"AMD64 Alpine Linux NoGIL 3.x\" buildbot: https://buildbot.python.org/#/builders/1819/builds/1699\n\nScript:\n\n```py\nimport threading\n\ndef recurse():\n    return recurse()\n\ndef outer():\n    try:\n        recurse()\n    except RecursionError:\n        pass\n\nw = threading.Thread(target=outer)\nw.start()\nw.join()\nprint('end of main thread')\n```\n\ngdb traceback:\n\n```\n(gdb) where\n#0  0x0000560e9bedb871 in _Py_Dealloc (op=0x20004156010) at Objects/object.c:3277\n#1  0x0000560e9bedb9ef in _Py_MergeZeroLocalRefcount (op=op@entry=0x20004156010) at Objects/object.c:444\n#2  0x0000560e9c088aaf in Py_DECREF (filename=filename@entry=0x560e9c12425b \"./Include/refcount.h\", \n    lineno=lineno@entry=520, op=0x20004156010) at ./Include/refcount.h:359\n#3  0x0000560e9c088af7 in Py_XDECREF (op=\u003coptimized out>) at ./Include/refcount.h:520\n#4  0x0000560e9c088e30 in tb_dealloc (op=0x20004156070) at Python/traceback.c:245\n#5  0x0000560e9bedb8e0 in _Py_Dealloc (op=0x20004156070) at Objects/object.c:3300\n#6  0x0000560e9bedb9ef in _Py_MergeZeroLocalRefcount (op=op@entry=0x20004156070) at Objects/object.c:444\n#7  0x0000560e9c088aaf in Py_DECREF (filename=filename@entry=0x560e9c12425b \"./Include/refcount.h\", \n    lineno=lineno@entry=520, op=0x20004156070) at ./Include/refcount.h:359\n#8  0x0000560e9c088af7 in Py_XDECREF (op=\u003coptimized out>) at ./Include/refcount.h:520\n#9  0x0000560e9c088e30 in tb_dealloc (op=0x200041560d0) at Python/traceback.c:245\n#10 0x0000560e9bedb8e0 in _Py_Dealloc (op=0x200041560d0) at Objects/object.c:3300\n#11 0x0000560e9bedb9ef in _Py_MergeZeroLocalRefcount (op=op@entry=0x200041560d0) at Objects/object.c:444\n#12 0x0000560e9c088aaf in Py_DECREF (filename=filename@entry=0x560e9c12425b \"./Include/refcount.h\", \n    lineno=lineno@entry=520, op=0x200041560d0) at ./Include/refcount.h:359\n#13 0x0000560e9c088af7 in Py_XDECREF (op=\u003coptimized out>) at ./Include/refcount.h:520\n#14 0x0000560e9c088e30 in tb_dealloc (op=0x20004156130) at Python/traceback.c:245\n#15 0x0000560e9bedb8e0 in _Py_Dealloc (op=0x20004156130) at Objects/object.c:3300\n#16 0x0000560e9bedb9ef in _Py_MergeZeroLocalRefcount (op=op@entry=0x20004156130) at Objects/object.c:444\n#17 0x0000560e9c088aaf in Py_DECREF (filename=filename@entry=0x560e9c12425b \"./Include/refcount.h\", \n    lineno=lineno@entry=520, op=0x20004156130) at ./Include/refcount.h:359\n#18 0x0000560e9c088af7 in Py_XDECREF (op=\u003coptimized out>) at ./Include/refcount.h:520\n#19 0x0000560e9c088e30 in tb_dealloc (op=0x20004156190) at Python/traceback.c:245\n#20 0x0000560e9bedb8e0 in _Py_Dealloc (op=0x20004156190) at Objects/object.c:3300\n#21 0x0000560e9bedb9ef in _Py_MergeZeroLocalRefcount (op=op@entry=0x20004156190) at Objects/object.c:444\n#22 0x0000560e9c088aaf in Py_DECREF (filename=filename@entry=0x560e9c12425b \"./Include/refcount.h\", \n    lineno=lineno@entry=520, op=0x20004156190) at ./Include/refcount.h:359\n#23 0x0000560e9c088af7 in Py_XDECREF (op=\u003coptimized out>) at ./Include/refcount.h:520\n#24 0x0000560e9c088e30 in tb_dealloc (op=0x200041561f0) at Python/traceback.c:245\n#25 0x0000560e9bedb8e0 in _Py_Dealloc (op=0x200041561f0) at Objects/object.c:3300\n#26 0x0000560e9bedb9ef in _Py_MergeZeroLocalRefcount (op=op@entry=0x200041561f0) at Objects/object.c:444\n#27 0x0000560e9c088aaf in Py_DECREF (filename=filename@entry=0x560e9c12425b \"./Include/refcount.h\", \n    lineno=lineno@entry=520, op=0x200041561f0) at ./Include/refcount.h:359\n#28 0x0000560e9c088af7 in Py_XDECREF (op=\u003coptimized out>) at ./Include/refcount.h:520\n#29 0x0000560e9c088e30 in tb_dealloc (op=0x20004156250) at Python/traceback.c:245\n#30 0x0000560e9bedb8e0 in _Py_Dealloc (op=0x20004156250) at Objects/object.c:3300\n#31 0x0000560e9bedb9ef in _Py_MergeZeroLocalRefcount (op=op@entry=0x20004156250) at Objects/object.c:444\n#32 0x0000560e9c088aaf in Py_DECREF (filename=filename@entry=0x560e9c12425b \"./Include/refcount.h\", \n(...)\n#3751 0x0000560e9be774fb in PyObject_Call (callable=\u003coptimized out>, args=\u003coptimized out>, kwargs=\u003coptimized out>)\n    at Objects/call.c:373\n#3752 0x0000560e9c10f6ef in thread_run (boot_raw=boot_raw@entry=0x20000030920) at ./Modules/_threadmodule.c:388\n#3753 0x0000560e9c0874c0 in pythread_wrapper (arg=\u003coptimized out>) at Python/thread_pthread.h:234\n#3754 0x00007f484b327573 in start (p=\u003coptimized out>) at src/thread/pthread_create.c:207\n#3755 0x00007f484b328ec1 in __clone () at src/thread/x86_64/clone.s:22\nBacktrace stopped: frame did not save the PC\n\n(gdb) info threads\n  Id   Target Id                  Frame \n  1    LWP 9804 \"python\"          __cp_end () at src/thread/x86_64/syscall_cp.s:29\n* 2    LWP 9807 \"Thread-1 (outer\" 0x0000560e9bedb871 in _Py_Dealloc (op=0x20004156010) at Objects/object.c:3277\n```\n\n`_Py_Dealloc()` has the `Trashcan` mechanism which is supposed to avoid long chain of `_Py_Dealloc()` calls to reduce the stack memory consumption. But it seems like it doesn't work on Alpine Linux (Python built with `musl` C library).\n\ngdb variables in the `_Py_Dealloc()` frame:\n\n```\n(gdb) p type->tp_name\n$6 = 0x555ba66f5c7f \"traceback\"\n\n(gdb) p gc_flag\n$7 = 16384\n```\n\nIn the parent `_Py_Dealloc()` frame:\n\n```\n(gdb) p type->tp_name\n$9 = 0x555ba66f5c7f \"traceback\"\n(gdb) p gc_flag\n$10 = \u003coptimized out>\n(gdb) p margin\n$11 = 115\n```\n\nIn the first `_Py_Dealloc()` frame (outer):\n\n```\n(gdb) p margin\n$12 = 119\n(gdb) p type->tp_name\n$13 = 0x555ba66e9dcd \"RecursionError\"\n(gdb) p gc_flag\n$14 = \u003coptimized out>\n(gdb) p type->tp_flags & (1UL \u003c\u003c 14)  # gc_flag\n$15 = 16384\n```\n\nOn a regular build (without Free Threading), the script works as expected, it displays:\n\n```\nend of main thread\n```\n\n\u003c!-- gh-linked-prs -->\n### Linked PRs\n* gh-149993\n* gh-150150\n* gh-151586\n\u003c!-- /gh-linked-prs -->\n","author":{"url":"https://github.com/vstinner","@type":"Person","name":"vstinner"},"datePublished":"2026-04-08T16:52:03Z","url":"https://github.com/python/cpython/issues/148260"}